Background Identifying differences and similarities between CLA+ polarized T-cell subsets in pediatric vs. adult atopic dermatitis (AD) is critical for directing new treatments towards children. Objective To compare activation markers and frequencies of skin-homing (CLA+) vs. systemic (CLA−) “polar” CD4 and CD8 T-cell subsets in early pediatric AD, adult AD and controls. Methods Flow cytometry was used to measure CD69/ICOS/HLA-DR frequency in memory subsets as well as IFN-γ, IL-13, IL-9, IL-17, and IL-22 cytokines, defining Th1/Tc1, Th2/Tc2, Th9/Tc9, Th17/Tc17, and Th22/Tc22 populations in CD4 and CD8 cells, respectively. We compared peripheral blood from 19 children <5 years and 42 adults with well-characterized moderate to severe AD, as well as age-matched controls (17 children and 25 adults). Results Selective ICOS activation (P<0.001) was seen in children. CLA+ Th2 T-cells were markedly expanded in both AD children and adults compared to controls, but decreases in CLA+ Th1 T-cells were greater in AD children (17% vs. 7.4%, P=0.007). Unlike in adults, no imbalances were detected in pediatric AD CLA− T-cells, nor were there altered frequencies of Th22 T-cells within CLA+ or CLA− compartments. Adults with AD had increased frequency of IL-22-producing CD4 and CD8 T-cells within the skin-homing population (9.5% vs. 4.5%; 8.6% vs. 2.4%, respectively; P<0.001) as well as increased HLA-DR activation (P<0.01). Conclusions These data suggest that Th2 activation within skin-homing T-cells may drive AD in children and that reduced counter-regulation by Th1 T-cells may contribute to excess Th2 activation. Th22 “spreading” of AD is not seen in young children and may be influenced by immune development, disease chronicity or recurrent skin infections. Clinical Implications Therapeutic approaches to treat AD in children may be best directed to correction of Th2/Th1 imbalance, while adults might also benefit from IL-22 targeted therapies.

Moderate to severe pediatric AD may be associated with central obesity and increased systolic BP.

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